A digital camera and a digital video camera with use of a solid state imaging device such as a CCD, a CMOS, and the like is in widespread use. A conventional solid state imaging device has a structure that an image sensor chip which is a semiconductor substrate is contained in a package and is sealed by a transparent glass rid. However, because of increasing demand for a mobile phone with the image-taking function and the like, the solid state imaging device is required to be small.
As a packaging method to downsize the solid state imaging device, a wafer-level chip size package (hereinafter WLCSP) is known. In the WLCSP, a semiconductor device is obtained by dicing a wafer after the packaging is completed in a semiconductor wafer process. A solid state imaging device manufactured by the WLCSP has the same size same as a bare chip.
Examples of the solid state imaging devices of WLCSP type are disclosed in Japanese Patent Laid-Open Publications No. 2002-329850 and No. 2003-163342, and a prior application of the applicant (Japanese Patent Application No. 2003-320271). In the Japanese Patent Laid-Open Publication No. 2002-329850, the solid state imaging device is formed in a way that a transparent cover glass is adhered on a frame which is formed of lamination of insulating resin and electrodes to surround an image sensor, so as to seal the image sensor. And a space between the image sensor and the cover glass is provided such that the condensing performance of the micro lens does not become worse.
In the Japanese Patent Laid-Open Publication No. 2003-163342, the solid state imaging device is formed such that a frame is formed by coating adhesive including filler around an image sensor, and then a transparent cover glass is adhered on the frame so as to seal the image sensor. And between the image sensor and the cover glass, a space determined by a diameter of the filler is provided. In the Japanese Patent Application No. 2003-320271, the solid state imaging device is formed such that a spacer as a frame surrounds an image sensor and a transparent cover glass is adhered on the spacer so as to seal the image sensor with appropriate space between the image sensor and the cover glass.
The solid state imaging devices described above are manufactured as described below. First, plural frames are formed on a transparent glass substrate which is a base material of the cover glass. Material of these frames is the insulating resin and the electrodes in the Japanese Patent Laid-Open Publication No. 2002-329850, while the adhesive including filler in the Japanese Patent Laid-Open Publication No. 2003-163342. In the Japanese Patent Application No. 2003-320271, the spacers are formed on the glass substrate and adhesive is applied on an end surface of the spacers. Next, the glass substrate and a wafer on which the plural image sensors and contact terminals are formed are joined such that the each image sensor is sealed by the frame and the glass substrate. Then the glass substrate with the wafer is diced into a plurality of the solid state imaging devices.
To increase the yield of the solid state imaging device manufacture, the wafer and the glass substrate should be free from sticking of the foreign matters. However, in the manufacturing methods of the Japanese Patent Laid-Open Publication No. 2002-329850 and No. 2003-163342 and the Japanese Patent Application No. 2003-320271, each manufacturing process is separated and the work needs to be transferred among respective manufacturing processes by human hands. Therefore, it is difficult to prevent that the foreign matters stick to the work.
In addition, in a process for coating the adhesive, the glass substrate is highly possible to be messed. However, in the Japanese Patent Laid-Open Publication No. 2002-329850, there is no statement about the process for coating the adhesive, therefore the possibility of messing the glass substrate in the coating process is not considered. In the Japanese Patent Laid-Open Publication No. 2003-163342, the adhesive including filler is coated on the glass substrate by printing. This method has problems that alignment of the printing position and control of coating thickness are very difficult. When the application quantity is not appropriate, it ends up with defective sealing. Further, it is possible that the adhesive slides or sticks to a portion of the glass substrate which faces to the image sensor at the time of printing, which leads to decrease in the yield ratio. In addition, if silicon is used as a material of the surface on which the adhesive is coated, there is possibility that the silicon sheds the adhesive because the silicon has bad wettability to the adhesive.
In the Japanese Patent Application No. 2003-320271, a transcribing film on which the adhesive is coated at constant thickness as an adhesive layer is superimposed on the glass substrate, and then the transcribing film is rolled up to be peeled off from top end of the glass substrate, such that the adhesive layer is transcribed on the spacers on the glass substrate. Accordingly, it is easy to control the coating thickness of the adhesive.
However, in the Japanese Patent Application No. 2003-320271, the plastic film is peeled by human hands. Therefore, there are problems that curvature of the transcribing film and angle between the film and the transcribing film, both of which largely affect performance of the peeling, are unstable in peeling. For example, if the curvature of the transcribing film is too small, the peeling cannot be performed smoothly. If the curvature is too large, membrane of the adhesive is created between the transcribing film and the spacer. The membrane bursts and splashes to mess the glass substrate when exceeds the viscosity of the adhesive.
In addition, if the wafer and the glass substrate are not in parallel with facing each other at the time of joining, their joining positions become misaligned. For example, when a parallelism between two 6-inch wafers is 60 μm, a misaligned distance between two wafers becomes 10 μm. In the solid state imaging device which has small size, the distance between the image sensor and the frame is also small. Accordingly, the adhesive flows to the image sensor and the contact terminals when the joining positions are slightly misaligned that causes deterioration of the yield. Therefore, the misaligned distance between the wafer and the glass substrate needs to be few micrometers or less. For satisfying the requirement, the parallelism between the two substrates needs to be 10 μm or less.
For adjusting the parallelism of the substrates 10 μm or less, the parallelism needs to be measured. As stated above, for preventing the sticking of foreign matters, the parallelism measurement should be performed in a non-contact way. Conventionally, the non-contact parallelism measurement is performed by laser displacement gauges. However, the solid state imaging device of WLCSP type, which uses opaque material for the spacer, can not be measured in parallelism by using the laser displacement gauges. Note that the Japanese Patent Laid-Open Publication No. 2002-329850 and No. 2003-163342 and the Japanese Patent Application No. 2003-320271 do not describe solutions for these problems in joining the substrates.
An object of the present invention is to provide a device and a method for joining a wafer (semiconductor substrate) and a glass substrate (sealing substrate) with high yield ratio.